The dual inverter drive system feeding an open-end winding permanent magnet (PM) motor has been studied for developing autopilot technologies of hybrid vehicles. Autopilot systems require fault-tolerant functions, which enable it to continue to drive the motor even if some failure occurs in the motor drive system. The fault-tolerant function of a dual inverter drive system, which assumes that the DC-bus battery power source of the dual inverter drive system has failed, is discussed in this paper. In the dual inverter drive system that is considered, both the inverters have a capacitor in parallel with a battery across each DC-bus. The capacitor drives the motor continuously even if the DC-bus battery has failed. The inverter, in which the DC-bus battery has failed, is operated with the capacitor instead of the failed battery. It is required to both control the capacitor voltage at a constant value and simultaneously generate multilevel voltage waveforms across the motor windings with the space vector modulation (SVM). In this paper, the fault-tolerant function of the DC-bus battery in a dual inverter drive system is proposed, and its operation characteristics are examined through several experiments and compared with those of a normal system.